The HIV-encoded aspartyl proteinase (HIV PR) is critical to the life cycle of the AIDS virus. Although an enormous effort has been put into the design of inhibitors of the HIV PR, there is relatively little fundamental knowledge of this important enzyme. It is the goal of this research to carry out basic studies of the HIV PR molecule, and to understand how the properties of this enzyme originate in its chemical structure, both covalent and folded/three dimensional. The long-term aims of this research are to provide a detailed understanding of the molecular principles by which the HIV PR recognizes its substrates and catalyzes their specific hydrolysis. Such understanding of how the HIV PR works will contribute to the design and evaluation of more effective enzyme inhibitors as potential AIDS therapeutics. The specific studies envisioned in this proposal can be divided into five categories: 1. improved total chemical synthesis of the HIV PR molecule (2 x 99 residue peptide chains; 21.5 kDa); 2. folding (including dimer formation) & thermodynamic stability; 3. substrate recognition; 4. catalysis; 5. redesign of enzyme action. In each of these areas the applicant will use the tools of chemistry to probe in hitherto unprecedented ways the structure-function relationships in HIV PR. The understanding arrived at will be tested by fundamental redesign of the enzyme to work on different substrates, under different conditions, and to use altered molecular structure to carry out new chemical reactions.